In LTE (Long Term Evolution) of the 3GPP (3rd Generation Partnership Project), HARQ-ACK or a RANK INDICATOR (hereinbelow referred to as “RI”) can be transmitted from a UE (User Equipment: mobile unit) to an eNodeB (base station) by a PUSCH that is used in data transmission.
In this explanation, a HARQ-ACK is an acknowledgement that indicates to the eNodeB whether downlink data that was transmitted from the eNodeB has been correctly received by the UE and has the two states of positive acknowledgement and negative acknowledgement.
On the other hand, an RI is an index that represents the rank of the downlink MIMO channel (the direction from the eNodeB to the UE) when performing MIMO (Multiple Input Multiple Output) communication between the UE and eNodeB and is reported to the eNodeB from the UE. The rank represents the number of communication paths that can be spatially multiplexed in MIMO communication, the upper limit being the lesser of the number of transmission antennas and the number of reception antennas that face each other. Each data communication path that has been spatially multiplexed is also referred to as a layer.
In Release 8 (2008 Edition) of LTE, the number of resources required when a UE transmits HARQ-ACK or RI to eNodeB on PSUCH is independently calculated by each UE and eNodeB, and the transceiving of the HARQ-ACK or RI is carried out together with recognition of the multiplexed resources.
By the way, in LTE, uplink resources are managed in two-dimensional space that is made up from a hypothetical frequency axis and time axis to enable similar treatment as downlink resources. In this hypothetical space, the frequency axis is partitioned in subcarrier units (15 kHz), the time axis is partitioned in SC-FDMA symbol units, and this partitioned area (grid) is referred to as resource elements (herein below represented as RE). The above-described number of resources represents the number of these RE.
In Release 8 of LTE, only PUSCH of one-antenna transmission (i.e., non-MIMO) is supported in uplink data transmission. The following Formula 1 is specified for calculating Q′, the number of resources that is necessary when transmitting O-bit HARQ-ACK or RI on this PUSCH (Non-Patent Document 1).
                              Q          ′                =                                  ⁢                  min          (                                    ⌈                                                O                  ·                                      M                    sc                                          PUSCH                      ⁢                                              -                                            ⁢                      initial                                                        ·                                      N                    symb                                          PUSCH                      ⁢                                              -                                            ⁢                      initial                                                        ·                                      β                    offset                    PUSCH                                                                                        ∑                                          r                      =                      0                                                              C                      -                      1                                                        ⁢                                      K                    r                                                              ⌉                        ,                          4              ·                              M                sc                PUSCH                                              )                                    [                  Formula          ⁢                                          ⁢          1                ]            Formula 1 is described hereinbelow.
The function min( ) on the right side, similar to a typical definition, is a function for selecting the minimum value among arguments.
Of the arguments of the function min( ), the argument of the first item is described.
M_sc^PUSCH-Initial represents frequency resources that have been allocated to data (transport block) that are to be transmitted by a PUSCH in units that correspond to subcarriers (i.e., 15 kHz units), and moreover, represents the resources that are allocated at the time of initial transmission to a transport block that is to be transmitted by a PUSCH in which HARQ-ACK or RI is multiplexed (regardless of whether the transmission is an initial transmission or a re-transmission).
Here, initial transmission represents transmission in which the transport block is first transmitted, and retransmission represents transmission in which a transport block is retransmitted when the transport block (data) could not be correctly received at the time of the first transmission in an eNodeB.
N_symb^PUSCH-Initial represents the number of SC-FDMA symbols at the time of initial transmission of the transport block.
K_r represents the number of bits contained in the rth code block (starting from 0) after the transport block has been divided into C code blocks for the purpose of turbo-coding. Accordingly, the denominator of the argument of the first item represents the number of all bits following division of the transport block into code blocks.
In Formula 1, the part obtained by dividing the product of M_sc^PUSCH-Initial and N_symb^PUSCH-Initial by the denominator can be interpreted as showing the number of resources necessary for transmitting one bit of a transport block after division into code blocks while satisfying required quality.
“O” represents the number of information bits of HARQ-ACK or RI that is multiplexed on the PUSCH.
β_offset^PUSCH represents a coefficient (or offset, or factor, or multiplying factor) that is necessary for satisfying transmission quality of HARQ-ACK transmission and RI transmission when the transmission quality of the transport block is taken as a reference, is a value set in advance according to the type of transmission object (HARQ-ACK or RI), and is shared by both the eNodeB and UE. Because the quality required for HARQ-ACK and RI differs, different values can be set.
On the other hand, the argument 4·M_sc^PUSCH of the second item of the min( ) function gives the maximum value of the number of resources that can be allocated to HARQ-ACK and RI on the PUSCH in which HARQ-ACK and RI are actually multiplexed.